"When she is released, we will make arrangements to interview her and find out what happened from her point of view," DePaepe said.

Kelly said the operator, who has been employed with the CTA for about a year, will be interviewed by the NTSB on Tuesday.

The train operator was walking, talking and answering questions afterward, fire officials said. She was taken to the hospital with injuries to her leg and later released.

"It's unfortunate that this happened," Kelly said. "It's not 100 percent [clear] exactly what happened and how all this was caused."

Thirty-two people were injured in the crash, none seriously.

Denise Adams was on the train when the crash occurred.

"I was on the fifth or sixth car on the train and I heard a boom, and when I got off, the train was all the way up the escalator," Adams said.

Another passenger, who didn't want to be identified, described a scene of confusion and chaos.

"I thought it was a hard break, but then it got even worse, and I felt the train come off the tracks," the passenger said. "It was chaos, people freaking out trying to find out what's happening."

Blue Line passengers are being shuttled back and forth between the O'Hare and Rosemont stops by bus, and the detours and delays are expected to be in place on Tuesday. Train service will run on a normal schedule between the Rosemont and Forest Park stops.